Difference between the training and the API call result

Dear FormX Team,

we are using your service via API. We created an extractor called Invoices for this reason. It tuns out several cases the extractor is not giving back the currency of the invoice. However when I drop the given invoice to the Smart Learning, it always returns with the correct currency.
Do we miss something? Why the API not capable to discover the currency?

Thanks:
Peter Baranyi